OM605 and OM606
The last Bosch injection diesel engines from Mercedes-Benz… DOHC, prechamber combustion, efficiency, responsiveness, and the well-known kle-kle-kle-kle idle sound.
Introduced in the 1990s, the OM605 and OM606 engine pair can be seen as updates to the earlier OM602 and OM603 engines. In keeping with the spirit of the era, they were equipped with several then-modern developments: an EGR valve, a throttle valve (to reduce engine braking), ECU-based engine management and—what will concern us here—EDC (Electronic Diesel Control).
The EDC system also brought a new injection pump. In principle it is similar to the earlier units, however throttle input is no longer transmitted via a cable but by a sensor–servo motor pair, and engine shutoff is handled by the same servo motor and an electric shutoff valve instead of the earlier vacuum-operated solution.
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| The old, fully mechanical injection pump - source: Peachparts.com |
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| The new EDC injection pump with the shutoff valve installed – source: Kleinanzeigen.de |
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| The shutoff valve |
The new injection pump also comes with a modified fuel filter housing and new, fully plastic fuel lines with clip-type connections instead of threaded fittings. In other words, the engine underwent a thorough redesign, even though at first—and perhaps even second—glance it appears unchanged.
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| One of the new-type fuel lines – it can be removed from the port by pressing in the horseshoe-shaped clip |
Unfortunately, the EDC system contains a large number of connections. Most of them are associated with components that many consider unnecessary and were introduced as part of the EDC system; as a result, many owners choose to bypass or eliminate certain elements. From a technical standpoint, the incoming fuel can go directly to the lift pump (which is the only pump that draws fuel from the tank), then to the main filter, and from there to the injection pump. Below is a “map” of the EDC fuel system, edited by yours truly.
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| EDC fuel system layout |
After 20–30 years of service, these engines are unfortunately often characterized by difficult cold starts. The reason is simple: the numerous connections—and the sealing rings inside the shutoff valve—age and no longer seal properly, thus, when the fuel that's heated up during operation starts to contract during the night, air can leak into the system. According to the official repair procedure, this requires replacement of the transparent fuel lines (approximately €5–8 per piece) and the shutoff valve itself (around €220). Naturally, this is not necessarily the case—unless these components are physically damaged, replacing the sealing rings alone is sufficient.
The procedure:
Remove the intake pipe, engine cover, and intake manifold. From the factory, the injector return line is routed through the intake manifold—do not tear it out (be sure to note its routing through the intake manifold and the valve cover). Before the intake manifold can be completely removed, disconnect the crankcase ventilation return hose from its fitting (on catalytic-converter-equipped engines, from the crankcase breather valve).
Remove the intake manifold brackets as necessary.
Part numbers:
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Intake pipe: A6041400812 (varies; this was correct in my case)
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Intake manifold: A6051400201 (varies; this was correct in my case)
(Crankcase ventilation hoses are part of the intake manifold) -
Engine cover: A6050100467 (varies; this was correct in my case)
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Intake pipe and intake manifold mounting bolts: N914021006015
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Engine cover mounting bolts: A6069900001
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Intake pipe to intake manifold sealing ring: A6051410160
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Intake manifold to cylinder head gaskets: A6041410160
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With the limited access gained, begin by pulling the transparent fuel lines out of the shutoff valve. This is done by pressing in the horseshoe-shaped plastic clip on the lines and pulling them straight off. Also disconnect the electrical connector from the shutoff valve.
After this, remove the two mounting screws and pull the valve out of the injection pump.
Replace the O-rings on the fuel line connections and the sealing ring between the injection pump and the shutoff valve.
Part numbers:
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Shutoff valve: A0000784449 (Bosch part number: 0 928 402 030)
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Heat exchanger → pre-filter line: A6050701432
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Pre-filter → shutoff valve line: A6050700732
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Shutoff valve → lift pump line: A6050700832
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Lift pump → main filter line: A6050701032
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Main filter → injection pump line: A6050701532
O-ring sizes:
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Fuel line connections: 8 ID × 2.5 mm (Viton material)
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Injection pump to shutoff valve seal: 12 ID × 2.5 mm (Viton material)
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On the removed shutoff valve, two pins can be seen at each end, securing recessed end caps. These pins can be driven out using a thin metal rod or drill bit.
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| Location of the four pins - they can be driven out from this direction |
Once the pins are removed, the recessed end caps can be gradually lifted out through the pin holes. After sufficient movement, the caps can be fully removed using the recess between the holes.
MARK THE POSITION AND ORIENTATION OF THE CAPS. They should be able to go in either way, but I've hear of stories which say otherwise.
Remove the old O-ring from the extracted caps and replace it.
O-ring size: 25 ID × 3 mm (Viton material)
Reinstalling the caps with the new O-rings will be more difficult—but this is a good sign, as it indicates proper sealing. Reinstalling the pins is definitely a two-person job.
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Reassemble everything in reverse order, paying attention to the following:
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The shutoff valve is bolted to the injection pump, whose housing is made of aluminum—be careful not to strip the threads.
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Do not forget to reconnect the crankcase ventilation hose.
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Do not forget to route the injector return fuel line through the correct passages in the intake manifold and valve cover and reconnect it to the return circuit.
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The transparent fuel lines are correctly installed when the horseshoe-shaped clip is loose and pulled outward, and the connectors have been pushed fully into the ports until they click.
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Consult the system diagram if in doubt.
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Why Viton O-rings?
Although Viton is among the more expensive options on the O-ring market, it is necessary due to biodiesel-containing fuels and the heat generated by the engine.
Viton offers excellent chemical resistance and heat resistance up to 200 °C, and also has self-extinguishing properties.
The original sealing rings were not made from this material, which is likely one of the reasons they have begun to fail en masse in these engines.
For checking and confirming OE numbers, I recommend using Partsouq.com, where after sharing your VIN number, you can browse a thorough part database for your specific car.
Related video: How to Overhaul the OM605/OM606 Fuel Shut Off Valve (O-Rings, Disassembly, Access Guide)
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